/* -------------------------------------------------------------------------
 *
 * pg_crc32c_sse42.cpp
 *	  Compute CRC-32C checksum using Intel SSE 4.2 instructions.
 *
 * Portions Copyright (c) 2020 Huawei Technologies Co.,Ltd.
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/common/port/pg_crc32c_sse42.cpp
 *
 * -------------------------------------------------------------------------
 */
#include "c.h"

#include "port/pg_crc32c.h"

#include <nmmintrin.h>

pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void* data, size_t len)
{
    const unsigned char* p = (const unsigned char*)data;
    const unsigned char* pend = p + len;

    /*
     * Process eight bytes of data at a time.
     *
     * NB: We do unaligned accesses here. The Intel architecture allows that,
     * and performance testing didn't show any performance gain from aligning
     * the begin address.
     */
#ifdef __x86_64__
    while (p + 8 <= pend) {
        crc = (uint32)_mm_crc32_u64(crc, *((const uint64*)p));
        p += 8;
    }

    /* Process remaining full four bytes if any */
    if (p + 4 <= pend) {
        crc = _mm_crc32_u32(crc, *((const unsigned int*)p));
        p += 4;
    }
#else

    /*
     * Process four bytes at a time. (The eight byte instruction is not
     * available on the 32-bit x86 architecture).
     */
    while (p + 4 <= pend) {
        crc = _mm_crc32_u32(crc, *((const unsigned int*)p));
        p += 4;
    }
#endif /* __x86_64__ */

    /* Process any remaining bytes one at a time. */
    while (p < pend) {
        crc = _mm_crc32_u8(crc, *p);
        p++;
    }

    return crc;
}
